Production of metallic magnesium



' Pat ented July 19, 1938 PATENT OFFICE PRODUCTION OF METALLIC MAGNESIUMKonrad Erdmann, Radenthein, Austria, assignor to American MagnesiumMetals Corporation,

Pittsburgh, Pa.

No Drawing. Application March 23, 1937, Serial No. 132,541. In AustriaApril 2, 1936 10 Claims. (or 7567) for producing metallic magnesium in apurified] form.

Other advantages will appear as the description proceeds.

As far back as in the eighties of the last century attempts were made toutilize the method of smelting with carbon, which plays so important apart in zinc technology, for the obtaining of magnesium also. Theseattempts came to grief,

however, owing to the reversibility of the reaction MgO+C=Mg+CO. For along time it Was even regarded as doubtful whether magnesia could bereduced at all with the aid of electrically heated carbon; scientificexperiments led. finally to the answering of this question in a positivesense (Slade, Journ. Chem. Soc, 1908, pp. 327 et seq.) but no practicalachievement followed from this knowledge. On the contrary, in view ofthe difficulties involved, the technique of magnesium production took aturn, about the year 1915, in the direction of aluminothermic andsilicothermic reduction, with the view of avoiding the formation ofcarbon monoxide from the reducing agent; with the same object in view itwas subsequently proposed to employ ferrosilicon and calcium carbide asreducing agents. The problem of smelting magnesium oxide with carbon,the cheapest available reducing agent, which had so long defiedsolution, was solved in principle only a few years ago, by the adoptingof a two-stage process in the first stage of which the mixture of gasesand magnesium vapor leaving the hot furnace is abruptly cooled down to atemperature below the solidification point of magnesium, and in this waycondensed topowder that is as far as possible free of oxide, and whichthen admits of conversion in the second stage to liquid magnesium,

after elimination of the carbon monoxide present, in different ways butpreferably by distilling out the metal in a vacuum.

The invention relates to the conversion -of magnesium oxide with carbonin this two-stage process, and consists essentially in-heating themagnesium dust obtained in the. first stage of the process, after havingbeen separated from uiider increased pressure.

carbon monoxide, in the presenceof reducing. agents that fulfill thecondition of not yielding gases having an oxidizing action upon mag]-nesium, to a temperature at which the reducing agent used withdraws theoxygen from the magnesium oxide still present in its original conditionor as re-formed by reversal of the reaction. The magnesium therebydisengaged in the form of vapor is then condensed to a liquid or soliddeposit.

By virtue of the fact that what is done in the second stage of theprocess is not simply to distil out the magnesium present, but tocomplete the reduction with the aid of reducing agents which yield nocarbon monoxide, a better 'magnesium yieldis obtained without renderingthe operation appreciably more diflicult. The added cost of the moreexpensive reducing agent of the last-mentioned type that has to be usedin the second stage according to the present invention is abundantlyoutweighed by the improved magnesium yield, in view of the fact that butsmall quantities of this reducing agent are required in this stage. -Theadditional expenditure in the matter of heat is not considerable, sincethe reduction temperature for all the reducing agents of this secondtype is far below the temperature at which the smelting of magnesiumoxide with carbon has to be carried out. It is therefore sufficient toheat the mixture of magnesium dust and reducing agent in the secondstage of the process to a temperature not very much above thedistillation temperature of magnesium at ordinary pressure, it beingalso possible to work Suitable reducing agents of this second type arefor example aluminium, silicon (or ferrosilicon) and calcium car-jinvention there are employed as initial material magnesiferous nativeproducts containing suitable oxides as natural concomitants, which isthe .case more particularly with calcined dolomite, the most readilyavailable magnesiferous raw material. When starting with this material,at the temperatures at which the smelting of magnesium oxide with carbonproceeds at a suitable rate (temperatures in excess of 1900 C.),simultaneously with the reduction of the magnesium oxide, there alsotakes place the formation of calcium carbide from the calcium oxidepresent; whichv amount by the addition of natural or artificialproducts, or some other oxide of a suitable nature, such as aluminiumoxide or silicon dioxide (e. g. in the form of sand), may be added. Inall cases it is equally possible to employ mixtures of suitable oxides.Any iron oxide present in the raw material or in the additions theretohas no harmful effect but isuseful. I

If there be'an excess of reducing agent in the mixture at thecommencement of the second stage of the process the surplus can beturned to account by the introduction of fresh quantities of magnesiumoxide.

The charge consisting of mixtures of the starting material with oxide oroxide mixture, and carbon, may be introduced into the practically emptyand highly heated reduction chamber in uniformly small portions inaccordance with the method forming the subject of my U. S. A.application Serial No. 755,888. If the starting materials used are richin' magnesium oxide proportionately to the non-volatileconcomitantspres- 'ent, it is possible with this method of operation to ensure thatthe formed reducing agents of the second type are carried along incompany with the concomitant substances into the, condensate by thevaporous and gaseous reaction products. In practising this method smallportions of the charge may for instance be thrown into the empty highlyheated reduction chamber in the form of briquettes, or alternatively,the charging mixture may be rendered plastic and slippery by theaddition of slight quantities of a liquid binding agent and fed into thereduction chamber from beneath in uniformly small amounts at a time.

If there be employed as reducing agent a metal which has a considerablevapor pressure at the working temperatures required for the smelting ofmagnesium oxide with carbon, or of which the boiling point lies actuallybelow these practical working temperatures, as is the case for examplewith aluminium, the metal passes over into the gaseous phase andtherefore also into the powdery condensate by direct vaporization duringthe reduction of the magnesium oxide with carbon. In this mode ofcarrying out the process the additional heat expenditure for thesimultaneous vaporization of the reducing agent in the first stage ofthe process is counterbalanced by the advantage that the reducing agentcan be introduced in the form of impure and coarsely comminuted scrap,for example in the form of aluminium chips, and yet be present in themagnesium dust formed by condensation, in an extremely finely dividedstate up to 'that of colloidal dispersion.

I use the term a non-carbonaceous reducing agent to exclude the use notonly of carbon but also of hydrocarbons.

I claim:

1. A process of producing magnesium which "comprises evolving magnesiumvapor from oxidic magnesium-containing material by thermal reductionwith the aid of a.carbonaceous matter and suddenly cooling thedisengaged vapor so as to condense magnesium in solid powdery form, thenseparating the powdery condensate from carbon monoxide formed during thereduction and heating said condensate in the presence of anon-carbonaceous reducing agent to a temperature above the boiling pointof magnesium enabling the non-carbonaceous reducing agent towithdraw-oxygen from ,the magnesium oxide still present in its originalcondition or as reformed by reversal of reaction, whereupon themagnesium is recovered by condensation.

2. A process of producing magnesium which comprises evolving magnesiumvapor from oxidic magnesium-containing material by thermal reductionwith the aid of a carbonaceous matter in the presence of a non-oxidizinggas, suddenly cooling the disengaged vapor so as to condense magnesiumin solid powdery form, then separating the powdery condensate fromcarbon monoxide formed during the (reduction and heating said condensatein the pr sence of a non-carbonaceous reducing agent to a temperatureabove the boiling point of magnesium enabling the non-carbonaceousreducing agent to withdraw oxygen from the magnesium oxide still presentin its original condition or as reformed by reversal of reaction,whereupon the magnesium is recovered by condensation. Y

3. A process of producing magnesium which comprises extracting magnesiumin the vaporous state from oxidic magnesium-containing material bythermal reduction with the aid of a carbonaceous matter in the presenceof a non-oxidizing gas, and suddently cooling the disengaged vapor so asto condense magnesium in solid powdery form; then separating the powderycondensate from carbon monoxide formed during the reduction and admixingsaid condensate with a noncarbonaceous reducing agent, and then heatingthe mixture to a temperature above the boiling point of magnesiumenabling the non-carbonaceous reducing agent to withdraw oxygen from themagnesium oxide still present in its original condition or as reformedby reversal of reaction, whereupon the magnesium is recovered bycondensation.

4. A process of producing magnesium which comprises extracting magnesiumin the vaporous state from oxidic magnesium-containing material bythermal reduction with theaid of a carbonaceous matter in the presenceof a non-oxidizing gas and suddenly cooling the disengaged vapor so asto condense magnesium in solid powdery form, then separating the powderycondensate from carbon monoxide formed during the reduction and admixingsaid condensate with a metallic reducing agent, and then heating themixture to a temperature abovethe boiling point of magnesium enablingthe metallic reducing agent to withdraw oxygen from the magnesium oxidestill by condensation, a mixture of finely divided magnesium andreducing agent, then separating the solid condensate from carbonmonoxide formed during the reduction and heating said condensate to atemperature above the boiling point of magnesium enabling the metallicreducing agent to withdraw oxygen from the magnesium oxide still presentin its original condition or as reformed by reversal of reaction,whereupon the magnesium is recovered by condensation.

6. A process oi producing magnesium which comprises extracting magnesiumin the state of vapor from oxidic magnesium-containing material bythermal reduction with the aid of a carbonaceous matter in the presenceof a non-oxidizing gas, while mingling the starting mixture ofmagnesium-bearing prime material and carbonaceous reducing agent withaluminium and then shock cooling the escaping gases and vapors toproduce, by condensation, a mixture of finely divided magnesium andaluminium, then separating the solid condensate from carbon monoxideformed during the reduction and heating said condensate to a temperatureabove the boiling point of magnesium enabling the metallic reducingagent to withdraw oxygen from themagnesium oxide still present in itsoriginal condition or as reformed by reversal of'reaction, whereupon themagnesium is recovered by condensation.

'7. A process as defined in claim in which a volatile reducing agent isgenerated from a compound reducible by carbon during reduction of theoxidic magnesium-containing prime material by the action of carbon.

8. A process of producing magnesium which comprises extracting magnesiumin the vaporous state from oxidic magnesium-containing material bythermal reduction with the aid of carbonaceous matter in the presenceoia non-oxidiz-- ing gas, while adding to the magnesium-bearing primematerial, together with an appropriate excess of carbon, substancescapable of being converted, at the reduction temperature, by-the actionof carbon into a non-carbonaceous reducing agent, and regulating thereduction of the magnesium-bearing prime material to be effected by thecarbonaceous reducing agent added, in such a manner that thenon-carbonaceous reducing agent generated during the reduction issubstantially carried along in company with the vaporous and gaseousproducts evolved by the said reduction, and then suddenly cooling thedisengaged vapor so as to produce a mixture of magnesium condensed in afinely divided condition with the non-carbonaceous reducing agentcarried over by the vapors and gases evolved; then separating the solidmixture from carbon monoxide formed during the reduction and heatingsaidmixture to a temperature above the boiling point of magnesium enablingthe non-carbonaceous reducing agent to withdraw oxygen from themagnesium oxide still present in its original condition or as reformedby reversal of reaction, whereupon the magnesium is recovered bycondensation.

9; A process as claimed in claim 8 in which there is employed as initialmaterial a magnesiferous native product containing a concomitant oxidecapable of being converted into carbide at temperatures which are nothigherthan those at which the smelting of magnesium oxide with carbonproceeds at a suitable rate.

10. A process as claimed in claim 8 in which native calcined dolomite ordolomitic magnesite is 'used as initial magnesiferous material.

KONRAD ERDMANN.

